1. Field of the Invention
The invention generally wireless telecommunications systems, and, more particularly, to flexible push-to-talk call set up in a wireless telecommunication system.
2. Description of the Related Art
In wireless telecommunication systems, push-to-talk (PTT) capabilities are becoming popular with service sectors. PTT can support a “dispatch” voice service that operates over standard commercial wireless infrastructures, such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), and global system for mobile communications (GSM). In a dispatch model, communication between endpoints (end user devices) occurs within virtual groups, wherein the voice of one “talker” is broadcast to one or more “listeners.” A single instance of this type of communication is commonly referred to as a dispatch call, or simply a PTT call. A PTT call is an instantiation of a group, which defines the characteristics of a call. A group in essence is defined by a member list and associated information, such as group name or group identification. In the absence of a wireless multicast channel, each group is formed by the combination of separate point-to-point connections between each endpoint and PTT servers manage the call. Each endpoint is also known as a client. Although, a PTT call is sent to all members of a group, most common use of the PTT call is between one user and another user. One-to-one PTT call represents 90% of all PTT calls.
FIG. 1 illustrates a prior art architecture 100 supporting PTT communications. The architecture includes the deployment of a single PTT server region in conjunction with a carrier's CDMA infrastructure and packet data network. Each region of the PTT servers is deployed over a specific portion of a carrier packet data network. The PTT server within the region may be routing traffic between one or more Packet Data Service Nodes (PDSNs) in the carrier network. A communication device 102 that supports the PTT feature is in communication with a base station (BS) 104. Each BS 104 may be in communication with one or more base transmission stations (BTS) 114. The base station 104 is in communication with a high speed network 106 and PTT communications received from the communication device 102 is sent through the base station 104 and the network 106 to a packet data service node (PDSN). The PDSN communicates with the high speed network 106 and a PTT server's network 108, which is connected to a PTT network 110. The PDSN forwards the PTT communications to a PTT server 112 in the PTT network 110.
The PTT server 112 handles PTT communications among members of a PTT group. The PTT server 112 receives a PTT communication from one member and forwards it to all members of the PTT group. The PTT communication is usually received as data packets from the network 110, and the PTT communication sent out by the PTT server 112 are also in data packet format. A packet data service node (PDSN) and a connected base station (BS) then established through a BTS 114 a dedicated channel to transmit the PTT communication to a receiving mobile client (a PTT member).
FIG. 2 illustrates a prior art message flow 200 for a PTT call set up. When a PTT user (originator) is ready to make a PTT communication, he presses a PTT activation button on his mobile device 102 and a PTT request is thus made. In response to the PTT request received by the mobile device 102, and the mobile device sends a call request to the PTT server 112, which is also known as the PTT dispatcher. The PTT server 112 receives the call request and process the call request. The call request processing includes identifying the PTT user, identifying a PTT group to which the PTT user belongs, identifying member of this PTT group, and preparing announce call messages to be sent to each member of the PTT group.
After the PTT server 112 sends the announce call messages, each announce call message is received by a PDSN and forwarded by the PDSN to a BS 104. The BS 104 broadcasts the announce call message to all the sectors covered by the BTS 114 connected to the BS 104. If a mobile client who is a targeted receiver is available, the mobile client sends an accept call message back to the PTT server 112. After receiving the accept call message from at least one mobile client, the PTT server 112 sends a floor grant message back to the originating mobile client. There may be more than one targeted user in the originator's PTT communication group, and the PTT server 112 will grant the floor to the originator if there is at least one targeted mobile client available. After receiving the floor grant message, the PTT requesting mobile client (originator) can then make a PTT communication.
The PTT communication set up process described above is time sensitive and the initial PTT latency shown in FIG. 2 is affected by network traffic. The long latency affects directly users of the PTT communication. Some attempts have been made to improve the set up process, and one way to speed up the PTT call set up process is to start the PTT call set up process earlier by anticipating the user's intent.
However, starting the PTT call set up earlier may not necessary save a lot time considering new technologies employed in the wireless communications network have already significantly reduced the call set up time. The early PTT call set up would be beneficial only if it takes a relatively long time for a wireless communications network to set up the PTT call. If fact, the early PTT call set up may tight up network resources while waiting for the user's actual PTT request. Therefore, it is desirous to have a system and method for flexibly enabling early PTT set up only when it is beneficial and without wasting network resources. It is to such system and method that this invention is primarily directed.